1. Field of the Invention
This invention relates to bagpipes and in particular to the pipe bag of the bagpipes.
2. Background of the Invention
Bagpipe bags are conventionally made from animal hide, and in particular sheepskin. The animal hide is cut and sewn into shape, then stocks are bound into each of five apertures to allow the connection of three drones, a mouthpiece, and a chanter. In use, the bag, which is inflated by the piper through the mouthpiece, supplies air to the drones and chanter, each of which employs a reed to convert the flow of air into sound.
Conventional bags have a number of disadvantages. First, moisture in the form of spittle and condensation from the piper's breath can collect in the bag causing the reeds to become damp and so affecting the pitch and tone of the instrument. This can be a serious problem during extended playing sessions. Secondly, the bags require a lot of maintenance, as frequent seasoning is necessary to keep the hide supple and airtight. Thirdly, binding a set of stocks into a bag can be a laborious, time-consuming process. Fourthly, the useful life of a bag can be significantly less than one year.
It has been proposed in British Patent Application 8964/71 (Canadian Pat. No. 961677) to make a pipe bag of polyvinyl chloride and to control the problem of collected moisture in the bag by fitting into the bag a sponge to absorb the moisture. It was suggested that from time to time the chanter could be removed and the sponge squeezed between the bag walls to expel most of the moisture. Such a proposal however appears unlikely to protect the reeds from becoming damp.
The term "Hydrophilic layer" as used herein is restricted to continuous layers, including closed cell foamed layers. These layers do not allow the flow of gases or liquids through open pore channels in the material but do transfer substantialyamounts of water through the layer by absorbing water on one side of the layer where the water vapour concentration is high, and desorbing or evaporating it on the opposite side of the layer where the water vapour concentration is low.
Hydrophobic, as used here, means that water will not spread on the material and wick into its porous structure. A drop of water placed on the surface of a highly hydrophobic layer will remain in the form of a nearly spherical bead with an advancing water contact angle greater than 90 degrees. Water vapor which evaporates or desorbs from the adjacent hydrophilic layer is free to flow or diffuse as a gas through the pores of a the hydrophobic layer to the exterior environment.
Moisture vapor transmission rates refer to values measured using a modified version of test method ASTM-E96-B in which the air gap between the surface of the water and the material to be tested is eliminated by inverting the cup to bring the water directly into contact with the surface of the test material. This modified test method is illustrated and described in full in U.S. Pat. No. 4,194,041.